Epoch 15, 2009 September 22. a) Core spectrum, where Qa represents the core and Qb the feature moving downstream. For comparisons, see Figure 4a. b) Core-shift vectors of all frequency pairs. Using component Qb makes the KQ core-shift vector point in the opposite direction. c) Power-law fit (red curve) using the Qb component. d) Core-shift vectors of all frequency pairs. Using component Qa, labelled as the core, gives a reasonable direction of the KQ core-shift vector. e) Power-law fit (red curve) using Qa as the core, but a better fit is obtained f) when the U band is excluded.